In general, such individual suspension devices are placed in rows and columns and are fixed to rigid slats constituting the platform. The elements are commonly symmetrical about a transverse midplane and about a longitudinal midplane, and their hardness is not uniform, depending on the slope imparted to the top plate.
WO 01/15572 describes an individual suspension device comprising a foot and a suspension structure in which the suspension structure, on its own and at rest, is in the form of a central ring having a plurality of resilient radial arms diverging therefrom. The ends of these arms have means for fixing to a ring of the foot. After these arm ends have been assembled to the ring of the foot, the arms take up the shape of spherical sectors that are separated by lateral openings, but they are then subjected to elastic stress, and in the event of one of the fixing means breaking, they necessarily return to a radial position.
DE 29 903 423 presents the state of the art closest to the invention and it provides a hollow suspension structure of spherical shape made out of a foam of resilient synthetic material, having holes at its top and bottom ends for fixing to the foot and to the top plate by means of clips. After assembly, the suspension structure is normally airtight, and it functions like a balloon. The problem which arises is that of providing leaktightness around the holes.